Clutches are widely used to couple driven rotary shafts to driving rotary shafts, i.e. to couple a load to a source of power. Because in most instances a driven shaft is initially at a standstill and a driving shaft is rotating when coupling, slippage occurs between engaging surfaces of the driven and driving members of the clutch while friction between these surfaces accelerates the driven shaft to the speed of the driving shaft during engagement of the clutch. This relative motion of slippage in the presence of friction generates heat.
A disc clutch is one type of clutch often provided in agricultural machinery. Such a disc clutch includes at least one generally disc-shaped driving member or pressure plate and at least one generally disc-shaped driven member or clutch plate. A spring is foreseen to keep the plates a distance from each other to prevent unwanted coupling. An actuator located within or upon the clutch forces the pressure plate against the clutch plate when clutch engagement is desired.
When a signal is given to the actuator to engage the clutch, the actuator has to overcome the pressure of the spring before the pressure plate actually starts to move towards the clutch plate. Once the force of the actuator is above the tension of the spring, the pressure plate will move towards the clutch plate until they make contact. The force by the actuator will then be increased, such that the plates will start to couple. When the angular speeds of the driven and driving members of the clutch are equal, engagement of the clutch is complete and the pressure of the actuator will be leveled such that the engagement between the plates is maintained.
However, when engaging the plates, the driven shaft generates a torque while speeding up the load. If this torque on the load is above the structural limitations of the load, the load itself might be damaged.